At present, mobile phones are providing diversified functions and thus are more and more often used in accessing the Internet. But the more functions a mobile phone provides, the more safety challenges are faced by the mobile phone. Therefore, it has become a common practice to install a firewall in a mobile phone.
In recent Android operating systems for mobile phone, functions of a firewall are implemented by using an iptable/netfilter module in the system kernel. In earlier versions of Android firmware, however, there is no such iptable/netfilter module, and many phone manufacturers add an iptable/netfilter module into mobile phones when compiling ROM (Read-Only Memory) of the mobile phones to enable the mobile phones to provide firewall functions.